This invention relates to an apparatus and method for non-destructively inspecting various solid bodies, such as drill bits used in oil exploration, for internal flaws or discontinuities.
In many industrial situations it is desirable to inspect a part or tool for internal flaws or discontinuities before use. The purpose of such inspection is to minimize the possibility of failure during use, due to such flaws or discontinuities.
Such internal flaws may result from the processes by which the part is manufactured and may manifest themselves as cracks, non-metallic inclusions, or other similar internal discontinuities. When a workpiece is used and thus stressed, failure can initiate at the discontinuity.
This is particularly true in the exploration for oil where drill-bits can fail at thousands of feet below the surface. Such failures can be very expensive and are time-consuming to correct.
Obviously, destructive testing, such as sectioning for internal examination, is undesirable since the part is destroyed and no longer useful.
Non-destructive testing techniques are available and include: (1) x-ray analysis which is potentially hazardous and may require time-consuming development of negatives; and (2) ultrasonic testing wherein an emitting transducer and a receiving transducer are used--this is sometimes referred to as pulse-echo analysis. In order to achieve an acceptable image of a flaw using the pulse-echo technique, electronic or computer processing is required. Such processing requires expensive equipment, careful set-up and complicated signal processing, particularly where irregularly shaped bodies are to be inspected.
It is therefore an object of this invention to provide a non-destructive testing technique for use in detecting internal flaws or discontinuities in various solid bodies which does not have the hazards or problems of X-rays or the cost and inconvenience of electronic or computer-assisted imaging.
A particular object of this invention is to provide a technique for inspecting oil drill-bits.
Acoustical technology, more specifically, ultrasonic technology, is well known for non-destructively inspecting bodies for internal flaws. See, for example, Gooberman's text entitled Ultrasonics Theory and Application, published by E.U.P. Limited [11, "Miscellaneous Applications on Ultrasonics," subsection 1.2 "Flaw Detection." That text discloses and discusses the general principles of the use of ultrasonics in inspection techniques.
In an effort to eliminate some of the problems associated with the pulse-echo techniques, work has been done to employ liquid crystals as the detector or receiver of the ultrasonic signal so as to provide an inexpensive real time display of the flaws. Prior to the development disclosed herein the work done in the liquid crystal field did not provide for a suitable, economic and commercial liquid crystal device, generally because of very poor quality images.
Liquid crystals are elongated, organic molecules whose properties are anisotropic (i.e., not uniform in every direction). This characteristic permits the liquid crystals to be selectively excited so as to provide an informative display. There are three main types of thermotropic liquid crystals, namely smectic, nematic and cholesteric. A discussion of such liquid crystals is presented in a publication by E. Merck of Darmstadt, Germany, entitled "Licristal"--liquid crystals. Other references on liquid crystal materials are available, such as de Genness Physics of Liquid Crystals, Oxford University Press 1974 and S. Chandrasekar, Liquid Crystals, Cambridge University Press, 1978.
Liquid crystals have found extensive use in non-emissive electro-optical displays, e.g., timepieces, calculators, etc. This development has been possible due to unique physical properties, such as anisotropic dielectric constants, conductivities, etc.
A study, identified as "Acousto-Hydrodynamic Effects in Liquid Crystals" authored by J. S. Sandhu, W. G. B. Britton, and R. W. V. Stephens, Physics Department, Chelsea College, London, United Kingdom, discusses the effect of acoustical surface waves on liquid crystals coupled to the surface of a body. In that study a liquid crystal material was applied directly to the surface of a body and a sonic transducer was also coupled directly to the surface of the body. The transducer caused sonic energy to travel along the surface to the liquid crystal. When the liquid crystal was observed through crossed polars (i.e., polarizers oriented at 90' to each other) optical changes in the liquid crystal enabled them to visualize surface waves (stripes with a separation equivalent to the wave length of the surface wave). However, clear visualization was only obtained at low acoustical intensities. At higher acoustical intensities, the liquid crystal started to flow (this is sometimes referred to as acoustic streaming) and destroy the picture. See J. S. Sandhu et al., Proceedings Institute of Acoustic, Spring meeting 1980 (G.B.).
The literature includes technical papers and publications which deal with combining liquid crystal technology and ultrasonic technology for generation of holograms and for flaw detection.
There are also many U.S. patents which deal with similar technology. See for example, Dreyer, U.S. Pat. No. 3,597,054; Kessler, U.S. Pat. No. 3,707,323; Greggus, U.S. Pat. No. 3,831,434; and Brenden, U.S. Pat. No. 3,879,989 which are representative of the state of the art.
None of the liquid crystal/ultrasonic systems which are disclosed in the prior art literature as patents provide an acceptable image of the flaw or discontinuity so that the system can be used on a real-time basis.
It is therefore an object of this invention to provide an ultrasonic system which uses liquid crystals for inspecting bodies and in which the image is satisfactory and of a high quality.
These and other objects of this invention will become apparent from the following description and appended claims.